US6654638B1 - Ultrasonically activated electrodes - Google Patents

Abstract

An implantable electrode, where the electrode comprises a first piezoelectric element which converts mechanical energy into electrical energy, and a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode. The mechanical energy for stimulating the piezoelectric element originates from a source external to the implantable electrode. In one embodiment, the external source is from a transmitter that is located on, or integrated into, either a cardiac lead and/or the implantable pulse generator. The electrode further includes an implantable housing into which is integrated the first piezoelectric element and on which is mounted the anode and the cathode. The housing also contains pacing control circuitry, which is coupled to the first piezoelectric element, the anode and the cathode. In one embodiment, the pacing control circuitry serves to receive the electrical energy generated by the first piezoelectric element and control the delivery of pacing level energy pulse between the anode and the cathode.

Description

FIELD OF THE INVENTION

This invention relates generally to medical devices, and more particularly to pulse generating systems.

BACKGROUND

Implantable pulse generators (e.g., pacemakers, implantable cardioverter/defibrillators) are integrated highly sophisticated electro-mechanical systems. They typically comprise at least one implantable cardiac lead coupled to a pulse generating device. The implantable cardiac leads serve to physically and electrically connect the pulse generating device, including the electronic circuitry housed within the device, to pacing electrodes positioned on the implantable cardiac lead. The implantable cardiac lead, therefore, acts as a tether to connect the pacing electrodes on the cardiac lead to the implantable pulse generating device.

Implantable cardiac leads typically include at least one pacing electrode, a lead conductor, lead insulation, and a lead connector. When one pacing electrode is present on the implantable cardiac lead, it is typically placed at the distal end of the lead. The lead conductor physically and electrically couples the pacing electrode to the electronic circuitry of the pulse generator. The lead conductor serves to conduct pacing level energy pulses from the electronic circuitry to the pacing electrode, and to conduct cardiac signals sensed by the pacing electrode to the electronic circuitry.

The lead conductor is housed within the lead insulation. The lead insulation electrically isolates the lead conductor, allowing the pacing level energy pulses from the pulse generator to be delivered to the pacing electrode and cardiac signals from the pacing electrode to be delivered to the electronic circuitry of the pulse generator. The lead connector also serves to physically couple the implantable cardiac lead to the housing of the pulse generator. Thus, the current state of the art for implantable pulse generators is to use the lead conductor to pass electrical pacing pulses to the pacing electrode when delivering pacing pulses to the heart.

The size of implantable cardiac leads is often a limiting factor in where the implantable cardiac lead can be positioned within the heart. Typically, implantable cardiac leads have been implanted through the venous side of the circulatory system, with the distal end of the cardiac lead being positioned in either the right ventricle or right atrium. Implantable cardiac leads can also be positioned adjacent the left atrium or left ventricle by placing the lead in the coronary sinus or great cardiac vein. Regardless of the location, the pacing electrodes are always tethered to the pulse generator by cardiac lead. As a result, sites available for cardiac pacing by implantable cardiac leads are limited. Thus, a need exists whereby implanted electrodes for delivering electrical energy to cardiac tissue need not be constrained by the presence of a cardiac lead.

SUMMARY OF THE INVENTION

The present subject matter removes the limitation of the pacing electrode being coupled, or tethered, to the implantable cardiac lead. In one embodiment, there are provided self-contained electrodes which are adapted to receive at least one signal from a transmitter. In response to receiving the at least one signal, the self-contained electrodes generate and deliver an electrical energy pulse. In one embodiment, the electrical energy pulses are pacing level energy pulses. Thus, the present subject matter allows for the physical connection between the implantable cardiac lead and the pacing electrode to be severed. By severing the physical connection between the implantable cardiac lead and the pacing electrode, the self-contained electrodes of the present subject matter are able to be placed at any number of locations within the cardiac tissue without the limiting constraint of the traditional implantable cardiac lead.

In one embodiment, present subject matter provides an implantable electrode, where the electrode comprises a first piezoelectric element which converts mechanical energy into electrical energy, and a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode. In one embodiment, the mechanical energy for stimulating the piezoelectric element originates from a source external to the implantable electrode. In one embodiment, the external source is from a transmitter that is located on, or integrated into, either a cardiac lead and/or the implantable pulse generator.

In one embodiment, the implantable electrode includes an implantable housing into which is integrated the first piezoelectric element. The housing also includes an anode and a cathode positioned the peripheral surface of the housing. The housing also contains pacing control circuitry, which is coupled to the first piezoelectric element, the anode and the cathode. In one embodiment, the pacing control circuitry serves to receive the electrical energy generated by the first piezoelectric element and control the delivery of pacing level energy pulse between the anode and the cathode.

In an additional embodiment, the implantable electrode can further include a potential energy source (e.g., an electrochemical cell) which supplies at least a portion of the energy necessary to pace the cardiac tissue. In addition to the potential energy source, the pacing control circuitry can further include a switch, where the switch is operated by the electrical energy generated by the first piezoelectric element. In one embodiment, the switch is activated so as to deliver a pulse between the anode and cathode when the switch receives electrical energy generated by the first piezoelectric element.

In an alternative embodiment, the implantable electrode can further include a second piezoelectric element which converts mechanical energy into electrical energy. When a first and second piezoelectric element are present, each element is selected to resonate in a different frequency range, so that the first piezoelectric element resonates at a first frequency range and the second piezoelectric element resonates at a second frequency range. The implantable electrode further includes both the switch and a capacitor. In one embodiment, the switch is coupled to the first piezoelectric element, the second piezoelectric element, the anode and the cathode, and the capacitor is coupled to the switch.

Electrical energy is generated by the first piezoelectric element when a first transmission at the first frequency range resonates the first piezoelectric element and electrical energy is generated by the second piezoelectric element when a second transmission at the second frequency range resonates the second piezoelectric element, where the electrical energy is stored in the capacitor. The switch is then used to cause the pacing level energy pulse to be delivered between the anode and the cathode when a predetermined pulse signal is detected. In one embodiment, the predetermined pulse signal is a predetermined frequency change in the first frequency range. Alternatively, the predetermined pulse signal is a predetermined frequency change in the first and second frequency ranges.

In an alternative embodiment, the pacing control circuitry includes a switch, where the switch is operated by the electrical energy generated by the first piezoelectric element, and a potential energy source, where the potential energy source is coupled to the switch and supplies electrical energy to be delivered between the anode and the cathode once the first piezoelectric element provides electrical energy to activate the switch.

These and other features and advantages of the invention will become apparent from the following description of the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows one embodiment of a system according to the present subject matter;

FIG. 2 shows one embodiment of a system according to the present subject matter;

FIG. 3 shows one embodiment of a system according to the present subject matter;

FIG. 4 shows one embodiment of a system according to the present subject matter;

FIG. 5 shows one embodiment of an electrode according to the present subject matter;

FIG. 6 shows one embodiment of an electrode according to the present subject matter;

FIG. 7 shows a block diagram of one embodiment of the present subject matter;

FIG. 8 shows a block diagram of one embodiment of the present subject matter; and

FIG. 9 shows embodiments of transmissions according to the present subject matter.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings which form a part hereof and in which is shown by way of illustration specific embodiments in which the invention can be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice and use the invention, and it is to be understood that other embodiments may be utilized and that electrical, logical, and structural changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense and the scope of the present invention is defined by the appended claims and their equivalents.

Implantable pulse generators (e.g., pacemakers, implantable cardioverter/defibrillators) are integrated highly sophisticated electro-mechanical systems. They typically comprise at least one implantable cardiac lead coupled to a pulse generating device. The implantable cardiac leads serve to physically and electrically connect the pulse generating device, including the electronic circuitry housed within the device, to pacing electrodes positioned on the implantable cardiac lead. The implantable cardiac lead, therefore, acts as a tether to connect the pacing electrodes on the cardiac lead to the implantable pulse generating device.

Implantable cardiac leads typically include at least one pacing electrode, a lead conductor, lead insulation, and a lead connector. When one pacing electrode is present on the implantable cardiac lead, it is typically placed at the distal end of the lead. The lead conductor physically and electrically couples the pacing electrode to the electronic circuitry of the pulse generator. The lead conductor serves to conduct pacing level energy pulses from the electronic circuitry to the pacing electrode, and to conduct cardiac signals sensed by the pacing electrode to the electronic circuitry.

The lead conductor is housed within the lead insulation. The lead insulation electrically isolates the lead conductor, allowing the pacing level energy pulses from the pulse generator to be delivered to the pacing electrode and cardiac signals from the pacing electrode to be delivered to the electronic circuitry of the pulse generator. The lead connector also serves to physically couple the implantable cardiac lead to the housing of the pulse generator. Thus, the current state of the art for implantable pulse generators is to use the lead conductor to pass electrical pacing pulses to the pacing electrode when delivering pacing pulses to the heart.

The size of implantable cardiac leads is often a limiting factor in where the implantable cardiac lead can be positioned within the heart. Typically, implantable cardiac leads have been implanted through the venous side of the circulatory system, with the distal end of the cardiac lead being positioned in either the right ventricle or right atrium. Implantable cardiac leads can also be positioned adjacent the left atrium or left ventricle by placing the lead in the coronary sinus or great cardiac vein. Regardless of the location, the pacing electrodes are always tethered to the pulse generator by cardiac lead. As a result, sites available for cardiac pacing by implantable cardiac leads are limited.

The present subject matter relates to a system that removes the limitation of a pacing electrode being coupled, or tethered, to an implantable cardiac lead. In one embodiment, there are provided self-contained electrodes which are adapted to receive at least one signal from a transmitter. In response to receiving the at least one signal, the self-contained electrodes generate and deliver to the heart an electrical energy pulse. In one embodiment, the electrical energy pulses are pacing level energy pulses. Thus, the present subject matter allows for the physical connection between the implantable cardiac lead and the pacing electrode to be severed. By severing the physical connection between the implantable cardiac lead and the pacing electrode, the self-contained electrodes of the present subject matter are able to be placed at any number of locations within the cardiac tissue without the limiting constraint of the traditional implantable cardiac lead.

FIG. 1 shows an embodiment of a system of the present subject matter. The system includes animplantable pulse generator10 to which is physically and electrically coupled atransvenous catheter14. In one embodiment, theimplantable pulse generator10 is a pacemaker. Alternatively, theimplantable pulse generator10 is an implantable cardioverter/defibrillator. In one embodiment, thetransvenous catheter14 includes atransmission element16, which is adapted to transmit mechanical signals. In one embodiment, the mechanical signals include signals in the ultrasonic frequency range. The system further includes animplantable pacing electrode18. Theimplantable pacing electrode18 receives the mechanical signals transmitted by thetransmission element16. In response to receiving the mechanical signals, theimplantable pacing electrode18 generates and/or produces electrical energy which this to be delivered between an anode and a cathode surface on theimplantable pacing electrode18. In one embodiment, mechanical signals from thetransmission element16 are transmitted to two or moreimplantable pacing electrodes18.

In one embodiment, theimplantable pulse generator10 of the present subject matter is an implantable pacemaker. Alternatively, theimplantable pulse generator10 of the present subject matter is an implantable cardiac defibrillator. In addition, thetransvenous catheter14 further includes one or more pacing electrodes and/or one or more defibrillation electrodes. One example is shown in FIG. 1 in which thetransvenous catheter14 is shown with a distaltip pacing electrode24. Additional pacing/sensing electrodes can also be positioned along the body of thetransvenous catheter14 and coupled to theimplantable pulse generator10 to allow for additional pacing and sensing activity.

In one embodiment, theimplantable pulse generator10 includes input circuitry to receive cardiac signals sensed by pacing electrodes, such as pacingelectrode24. The input circuitry is coupled to morphology analyzing circuitry which analyzes cardiac signals received through the input circuitry. In one embodiment, one or more electrochemical batteries are housed within theimplantable pulse generator10 and supply electrical energy to output circuitry for delivering pacing level energy pulses to the pacing electrodes coupled to thetransvenous catheter14 under the control of the morphology analyzing circuitry. Theimplantable pulse generator10 further includes transmission circuitry coupled to the output circuitry for supplying energy to thetransmission element16.

Upon receiving the energy from the transmission circuitry, thetransmission element16 produces one or more mechanical signals which are transmitted from thetransmission element16. In one embodiment, thetransmission element16 is a piezoelectric element which is adapted to cause mechanical energy to be delivered to theimplantable pacing electrode18 so as to allow theimplantable pacing electrode18 to generate and deliver one or more electrical pulses.

FIG. 1 shows one embodiment where thetransmission element16 is located along the body of thetransvenous catheter14. Thetransmission element16 is positioned along thetransvenous catheter14 to allow for thetransmission element16 to be positioned in any number of locations within a heart which is accessible to atransvenous catheter14. For example, thetransmission element16 is positioned along thecatheter14 to allow for theelement16 to be positioned within a right atrial chamber of the heart. In an alternative embodiment, thetransmission elements16 can be positioned along thetransvenous catheter14 to position the transmission element in any number of locations accessible to a transvenous catheter. For example,transmission element16 can be located along thetransvenous catheter14 to position the transmission element in a supraventricular location of a heart. In an additional embodiment, thetransmission element16 may be located along thetransvenous catheter14 at or adjacent adistal end32 of thetransvenous catheter14.Transvenous catheter14 could then be inserted through the coronary sinus vein to locate thetransmission element16 adjacent to either the left atrial chamber of the left ventricular chamber of the heart.

Theimplantable pacing electrode18 is adapted to receive mechanical energy transmitted from a transmission source which is external of theimplantable pacing electrode18. In one embodiment, the transmission source is thetransmission element16 located along thetransvenous catheter14. In an alternative embodiment, the transmission source is located within or on thehousing34 of theimplantable pulse generator10. In an alternative embodiment, the transmission source is located at a remote site which is neither on thetransvenous catheter14 or associated with thehousing34. Upon receiving the mechanical energy, theimplantable pacing electrode18 converts the mechanical energy into electrical energy. The electrical energy generated within theimplantable pacing electrode18 is then used to cause a pacing level electrical energy pulse to be delivered across an anode and a cathode position on theimplantable pacing electrode18.

In one embodiment, the mechanical signal is an ultrasonic signal transmitted from thetransmission element16. In one embodiment, thetransmission element16 is a piezoelectric element, where the piezoelectric element is coupled to the transmission circuitry located within theimplantable pulse generator10. The transmission circuitry is adapted to drive thetransmission element16 to produce an ultrasonic signal from the piezoelectric element. In one embodiment, the ultrasonic signal produced by thetransmission element16 is transmitted omnidirectionally. The directionality of ultrasonic transmission from a piezoelectric element depends on its physical dimensions (size and aspect ratio), its transmission mode (full wave, ¼ wave, etc.), and its coupling with the conduction medium. In one embodiment, the transmission element is constructed to transmit directionally and the ultrasonic signal produced by thetransmission element16 is directed in the direction of the implanted pacingelectrode18. In an alternative embodiment, the element is constructed to have less directional transmissions so that one or more pacing elements might be affected. In one embodiment, the transmission element delivers energy in a low frequency range, where a low frequency range is approximately one to five (1 to 5) megahertz, where one (1) megahertz is an acceptable value.

Besides being located on the catheter or within the housing of theimplantable pulse generator10, thetransmission element16 can be mounted within theheader36 of theimplantable pulse generator10. In a further embodiment, thetransmission element16 is coupled to theimplantable pulse generator10 through the use of an electrical lead, when thetransmission element16 is positioned subcutaneously in a position adjacent the heart of the patient.

In one embodiment, theimplantable pacing electrodes18 includes a piezoelectric element that is tuned to resonate in a specific frequency range. Atransmission element16 is provided that transmits ultrasonic frequencies in the resonance frequency range of theimplantable pacing electrode18. Upon receiving the ultrasonic signal, the piezoelectric element of theimplantable pacing electrode18 generates electrical energy which is used to cause a pacing level energy pulse to be delivered between an anode and a cathode on the implantable pacing electrode.

In an additional embodiment, more than one transmission element (e.g., more than one piezoelectric element) can be utilized in developing the ultrasonic signal to activate theimplantable pacing electrode18. For example, a first transmission element is positioned on theimplantable pulse generator10, and a second transmission element is positioned on thetransvenous catheter14. Alternatively, a first transmission element is located on or within theimplantable pulse generator10 and a second transmission element is coupled through a lead to theimplantable pulse generator10 and implanted subcutaneously adjacent to the heart. Other combinations of two or more transmission elements are also possible and considered within the scope of the present subject matter. Furthermore, each of the transmission elements can be adapted to transmit a signal at an individualized frequency range. For example, a first transmission element is adapted to transmit a first signal in a first frequency range and a second transmission element is adapted to transmit a second signal in a second frequency range. Each of the one ormore elements18 is then adapted to respond to the first and second frequency ranges as will be more fully described below.

Referring now to FIG. 2 there is shown an additional embodiment of the present subject matter. FIG. 2 shows theimplantable pulse generator10 coupled to thetransvenous catheter14 and to asecond transvenous catheter200. Thesecond transvenous catheter200 includes at least one pacing electrode physically and electrically coupled to theimplantable pulse generator10. In the embodiment, thesecond transvenous catheter200 is implanted in the supraventricular region of the heart to allow for cardiac signals to be sensed from and pacing pulses to be delivered to the supraventricular region of the heart. In an alternative embodiment, thesecond transvenous catheter200 is adapted to be implanted through the coronary sinus vein to position the pacing electrodes adjacent to the left atrium or to the left ventricular region of the heart. In an additional embodiment, thesecond catheter200 can include two or more pacing electrodes, where such catheter structures are known and are considered to be within the scope of the present subject matter.

In one embodiment, thetransvenous catheter14 and thesecond transvenous catheter200 are implanted into the heart and then coupled to theimplantable pulse generator10. Theimplantable pulse generator10 is then implanted subcutaneously in the body. In one embodiment, thetransvenous catheter14 includes a distaltip pacing electrode202 and asecond pacing electrode204. In one embodiment, thesecond pacing electrode204 is an annular or semi-annular ring electrode which is positioned proximal to the distal tip of pacingelectrode202 to allow for bipolar pacing and sensing from thetransvenous catheter14. Thesecond transvenous catheter200 also includes adistal tip electrode206. Thedistal tip electrode206 can be used for unipolar sensing and pacing between thedistal tip electrode206 and thehousing208 of theimplantable pulse generator10.

In the embodiment of FIG. 2, theimplantable pulse generator10 is shown having thetransmission element16 associated with thehousing208 of theimplantable pulse generator10. In one embodiment, thetransmission element16 is positioned within thehousing208 of theimplantable pulse generator10. Additionally, thetransmission element16 can also be positioned on or within aconnector block214 of theimplantable pulse generator10. In addition to associating thetransmission element16 with thehousing208, matching layers of material are used in association with thetransmission element16 to improve the acoustic coupling between the piezo-electric crystal (one possible material for the transmission element16) and the conducting medium (i.e., the body). Additionally, matching layers can be added to additional portions of theimplantable pulse generator10 which are in contact with tissue. Regardless of the position of thetransmission element16, the output of thetransmission element16 is directed towards theimplantable pacing electrodes18.

In the embodiment shown in FIG. 2, two or moreimplantable pacing electrodes18 positioned within a transmission range of thetransmission element16. In one embodiment, the two or moreimplantable pacing electrodes18 are implanted within a heart. When two or moreimplantable pacing electrodes18 are used, eachimplantable pacing electrode18 includes a piezoelectric element that is tuned to resonate at a different frequency. In one embodiment, this allowsimplantable pacing electrodes18 to be selectively paced by transmitting mechanical signals of theimplantable pacing electrode18 specific resonate frequency from thetransmission element16. In one embodiment, atransmission element16 can deliver a series of signals having different frequencies where each frequency triggers or causes separateimplantable pacing electrode18 elements to deliver pacing pulses to the heart28. This type of configuration allows two or moreimplantable pacing electrodes18 to deliver pacing pulses in an ordered or specific pattern. In one embodiment, selectively and sequentially activating two or moreimplantable pacing electrodes18 allows the heart to contract in a more forceful and efficient matter.

In an additional embodiment, two or moreimplantable pacing electrodes18 can be implanted in the supraventricular region and in the ventricular region of the heart. Theimplantable pacing electrodes18 implanted in the supraventricular region can be tuned to resonate at a first frequency, and theimplantable pacing electrodes18 implanted in the ventricular region can be tuned to resonate at a second frequency. Thetransmission element16 can then transmit a first signal to cause theimplantable pacing electrodes18 implanted in the atria to deliver a first pacing pulse. Thetransmission element16 can subsequently deliver a second signal to cause theimplantable pacing electrodes18 implanted in the ventricular region to deliver a second pacing pulse. In addition to including multipleimplantable pacing electrodes18, two ormore transmission elements16 can be included with two or moreimplantable pacing electrodes18. In one embodiment, each of the two ormore transmission elements16 can be tuned to deliver signals in frequency ranges that correspond to the different frequency ranges, or resonate frequencies of theimplantable pacing electrodes18. In this manner, each of thetransmission elements16 can be designated for one or more of theimplantable pacing electrodes18 implanted in the heart28.

Referring now to FIG. 3 there is shown an embodiment of a block diagram of animplantable pulse generator10. Theimplantable pulse generator10 includeselectronic control circuitry300 for receiving cardiac signals from the heart and delivering electrical energy to the heart. In one embodiment, pacing electrodes located on the transvenous catheter are electrically connected to input circuitry304 by the lead conductors housed within thetransvenous catheter14. In one embodiment, the input circuitry304 includes electrical surge protection circuitry and one or more amplifiers as are known. In one embodiment, the one or more amplifiers are electrically connected to cardiacwave detection circuitry308 bybus310. In one embodiment, the cardiacwave detection circuitry308 includes an R-wave detector when a transvenous catheter is implanted in the right ventricle chamber of the heart. The cardiacwave detection circuitry308 can also include a P-wave detector when a second transvenous catheter is implanted in the supraventricular region of the heart and then coupled to theimplantable pulse generator10. These components serve to sense and amplify the R-waves and P-waves of the heart and apply signals indicative thereof to morphology analyzingcircuitry312.

In one embodiment, themorphology analyzing circuitry312 is a programmable microprocessor-based system, which contains memory circuitry having parameters for various pacing and sensing modes. Themorphology analyzing circuits312 also store data indicative of the cardiac signals received by the input circuitry304. Communications circuity316 is additionally coupled to themorphology analyzing circuitry312 bybus310.Communications circuitry316 allows theimplantable pulse generator10 to communicate with aprogrammer unit320. In one embodiment,communications circuit316 and theprogrammer unit320 use a wire loop antenna and a radio frequency telemetry link, as is known in the art, to receive and transmit command signals and data to and from theprogrammer unit320 and theelectronic control circuitry300. In this manner, programming commands or instructions are transferred to theelectronic control circuitry300 of theimplantable pulse generator10.

Themorphology analyzing circuitry312 responds to sense cardiac signals by providing signals to output control circuitry324. In one embodiment, the output circuitry324 provides pacing level electrical energy to the heart. Power to theimplantable pulse generator10 is supplied by apotential energy source328 which is housed within theimplantable pulse generator10. In one embodiment, thepotential energy source328 is a electrochemical battery as is known in the art. Theelectronic control circuitry300 further includestransmission circuitry340. In one embodiment,transmission circuitry340 controls the mechanical signals delivered by one or more of the transmission elements. In one embodiment, thetransmission circuitry340 controls which transmission element is activated, how long the transmission element is activated, and at what level of intensity the transmission element is activated. Thetransmission circuitry340 is coupled to theelectronic control circuitry300 and receives command and control signals from themorphology analyzer312 bybus310. Themorphology analyzing circuitry312 responds to cardiac signals sensed within the heart by providing signals to either the output circuitry324 or to thetransmission circuitry340 to cause pacing level energy pulses to be delivered to the heart through either the pacing electrodes attached to one or more transvenous catheters and/or theimplantable pacing electrodes18.

In one embodiment, theelectronic control circuitry300 of theimplantable pulse generator10 is encased and hermetically sealed in ahousing330 suitable for implanting in a human body. Aconnector block334 is additionally attached to the housing of theimplantable pulse generator10 to allow for physical and electrical attachment of one or more transvenous catheters and the electrodes to theimplantable generator10 and the encasedelectronic control circuitry300.

In one embodiment, thetransvenous catheter14 includes a distal tip pacing electrode. This allows the transvenous catheter to sense rate signals, or near field signals, from the ventricle region of the heart. In an alternative embodiment, two or more pacing electrodes can be included on thetransvenous catheter14 to allow for bipolar sensing and pacing. In an additional embodiment, pacing electrodes can be located on both a first transvenous catheter and a second transvenous catheter when two catheters are implanted into the heart. This allows for near field signals to be sensed both from the ventricle and the supraventricular region of the patient's heart. Other intracardiac catheter arrangements and configurations known in the art are also possible and considered to be within the scope of the present system.

Referring now to FIG. 4, there is shown several embodiments of a transmission element in association with animplantable pulse generator10. In one embodiment, thetransmission circuitry340 is coupled to atransmission element400 which is positioned within thehousing410 of theimplantable pulse generator10. The transmission element could also be positioned on an exterior portion of thehousing410 of theimplantable pulse generator10. Atransmission element430 is shown coupled to thetransmission circuitry340 through the use of atransmission lead440. Thetransmission lead440 physically and electrically couples thetransmission element430 to thetransmission circuits340 through the use of theconnector block450. Thetransmission element430 can be implanted subcutaneously at a position adjacent the heart. Alternatively, thetransmission element430 can be positioned subcutaneously in any position that allows for the mechanical signal to best reach the implanted pacing electrodes of interest. As previously mentioned, one or more transmission elements can also be positioned within or on theconnector block450. Also, matching layers can be used in conjunction with thetransmission element430, as previously described.

Referring now to FIG. 5, there is shown an embodiment of theimplantable pacing electrode18. Theimplantable pacing electrode18 includes acathode500 and ananode502. Theimplantable pacing electrode18 includes ahousing504. In one embodiment, thehousing504 is the piezoelectric element of theimplantable pacing electrode18. Alternatively, the piezoelectric element is contained within thehousing504. The piezoelectric element is adapted to receive mechanical energy and convert the mechanical energy into electrical energy where the mechanical energy originates from a source external to theimplantable pacing electrode18. In one embodiment, the external source is thetransmission element16 previously described. In an alternative embodiment, the external source is a source located outside of the patient's body. The electrical energy generated by the piezoelectric element then causes a pacing level energy pulse to be delivered between thecathode500 and theanode502.

Thehousing504 is constructed of a material suitable for implanting into the human body. In one embodiment, thehousing504 is a cylinder, or elongate segment, of piezoelectric element, where circuitry for controlling theimplantable pacing electrode18 is contained within the cylinder. The piezoelectric element can also have matching layers to improve the acoustic coupling between the element of theelectrode18 and the tissue in which it is embedded. In an alternative embodiment, the piezoelectric and control circuitry are embedded inhousing504 which is constructed of an acoustically conductive material, such as an epoxy resin.

In an additional embodiment,implantable pacing electrode18 includes an active fixation element. In one embodiment, the active fixation includes tines positioned on the peripheral surface of theelectrode18. Alteratively, a hook can be used, where the hook can have, or be, either the anode or cathode of theelectrode18. Additionally, the hook can include one or more barbs. In one embodiment, theelectrode18 is approximately five (5) to fifteen (15) millimeters in length (along longitudinal axis) and approximately one (1) to four (4) millimeters in diameter. In one embodiment, the electrode is six (6) millimeters in length and has a diameter of three (3) millimeters. Additionally, theelectrode18 can have any number of shapes including, but not limited to, spherical, tubular, cylindrical, and elliptical. In an alternative embodiment, theimplantable pacing electrode18 can have any shape that is suitable for housing the pacing control circuitry and the piezoelectric element, and which has a peripheral surface that is suitable to accept an anode and a cathode of sufficient size and shape to deliver pacing energy pulses.

In one embodiment, the piezoelectric element of theelectrode18 is tuned, or selected, to resonate in a low frequency range, where the low frequency range is approximately in the range of between 1-5 megahertz, where one megahertz is an acceptable value. Alternatively, the frequency range is approximately 250 kilohertz to 20 megahertz, where 750 kilohertz to 7.5 megahertz is a range to be used. Additionally, the pacing pulses generated by theimplantable pacing electrode18 are controlled by delivering short duration pulses of ultrasonic energy, where each pulse of ultrasonic energy is used to create a pacing level pulse by theimplantable pacing electrode18. For example, it is known that cardiac tissue may be stimulated with a small pacing pulse of 2 milliseconds that delivers 5 to 10 microjoules. If the receiver only received energy during the 2 millisecond pacing pulse duration, then it would need to receive 2.5 to 5 microjoules per millisecond which is a reception power of 2.5 to 5 milliwatts. Assuming no losses, if the receiver had a 30 square millimeter cross-sectional area (e.g., 5 millimeter wide by 6 millimeter long) and was 5 centimeter from an omni-directional transmitter, then the transmission power would need to be about 2.5 to 5 Watts. In one embodiment, the short duration pulses are programmable values in the range of 0.5 to 10 millisecond, where 2 milliseconds is an acceptable value.

In an alternative embodiment, instead of delivering the pacing pulses only while the ultrasonic transmission from the transmission unit is underway, the implanted pacingelectrode18 stores the received energy over time and then delivers that energy as a pacing pulse when the transmission is stopped (e.g., when the transmission has stopped for approximately 10 milliseconds, the stored energy is delivered as a pacing pulse). With a maximum pacing rate of approximately 180 beats/minute, the same no-losses calculations requires the transmission power to be about 30 milliwatts or less. In one embodiment, circuitry in the implanted pacing electrode that is powered by the stored energy, detects the presence of a period without transmissions and then delivers the stored energy as a pacing pulse. In one embodiment, the charging duration and transmission power is timed to a cardiac cycle so as to ensure that theimplantable pacing electrode18 is prepared to deliver a pacing pulse when necessary.

Referring now to FIG. 6, there is shown one embodiment of theimplantable pacing electrode18 the present subject matter. In one embodiment, theimplantable pacing electrode18 includes acathode600 and ananode604. Theimplantable pacing electrode18 further includes ahousing608 that is suitable for implantation into the cardiac tissue of a human. As previously described, thehousing608 can be constructed of the piezoelectric element. Theanode604 and thecathode600 are positioned on the peripheral surface of thehousing608. Mounted within thehousing608 is pacingcontrol circuitry612. Thepacing control circuitry612 is coupled to theanode604 and thecathode600 and the piezoelectric element, where in this embodiment the piezoelectric element is thehousing608. The piezoelectric element receives mechanical energy from a source external to theimplantable pacing electrode18 and generates electrical energy to cause a pacing level energy pulse to be delivered between thecathode600 and theanode604. In the present embodiment, a fullwave bridge rectifier622 is used with the piezoelectric element to generate the pacing level energy pulse.

Referring now to FIG. 7, there is shown an alternative embodiment ofpacing control circuitry700. In one embodiment, thepacing control circuitry700 includes apiezoelectric element702, where thepiezoelectric element702 is electrically coupled to thepacing control circuitry700. Thepacing control circuitry700 further includes aswitch706 and apotential energy source708. Thepiezoelectric element702 and thepotential energy source708 are electrically coupled to theswitch706. In the present embodiment, thepiezoelectric element702 is used to generate a switching signal, where the switching signal is the electrical energy generated from thepiezoelectric element702. Upon receiving mechanical energy from a transmission element, thepiezoelectric element702 transmits the switching signal to theswitch706. After receiving the switching signal, theswitch706 is switched on, causing electrical energy to flow from thepotential energy source708 which causes a pacing level energy pulse to be delivered across the cathode and anode to the heart. In one embodiment, theswitch706 is a metal oxide semiconductor field effect transistor.

In one embodiment, thepotential energy source708 is an electrochemical battery. In an alternative embodiment, thepotential energy source708 is created by a half-cell potential difference between the metal of the anode and the metal of the cathode. In an alternative embodiment, thepotential energy source708 is a recharged on a beat-to-beat basis by the half-cell potential difference between the surrounding interstitial fluids and the metals of the anode and cathode. Metals useful for the present subject matter include, but are not limited to, platinum-iridium, titanium, gold, and/or stainless steel.

In a further embodiment, the pacing control circuitry includes a capacitor, where the electrical energy generated by the half cell potential is stored in the capacitor. The electrical energy stored in the capacitor is then delivered to the heart as a pacing pulse when the piezoelectric element delivers the switching signal to theswitch706. In an additional embodiment, the implantable electrode further includes a third electrode positioned on the peripheral surface of the implantable housing, where the third electrode is constructed of a metal that is different than the anode or the cathode metal. In one embodiment, the third electrode is composed of a metal that provides a larger half cell potential between the anode or the cathode than is possible between the cathode and anode.

In an additional embodiment, theimplantable pacing electrode18 includes two piezoelectric elements, where each piezoelectric element has a different resonance frequency. The two piezoelectric elements are coupled to the pacing control circuitry where the first piezoelectric element and the second piezoelectric element can receive mechanical signals from the transmission element, or elements, to charge the capacitor. In one embodiment, the transmission element, or elements, alternates transmitting ultrasonic energy that is suitable for resonating the first piezoelectric element and transmitting ultrasonic energy that is suitable for resonating the second piezoelectric element. In other words, the transmission element sends out ultrasonic frequencies that alternate between frequencies that resonate the first piezoelectric element and the second piezoelectric element. As each of the piezoelectric elements are excited they generate electrical energy to charge the capacitor which is coupled within the pacing control circuitry.

When a pacing pulse is to be delivered to the heart, the transmission element(s) delivers ultrasonic energy at a frequency that will resonate both the first piezoelectric element and the second piezoelectric element simultaneously. When both piezoelectric elements are excited simultaneously, the signals are then used to activate theswitch706 causing the energy stored in the capacitor to be delivered and pace the cardiac tissue of the patient. It is recognized that the two frequencies would need to be sufficiently different so that ultrasonic energy delivered at a first frequency to resonate a first piezoelectric element would not significantly effect a second piezoelectric element that is adapted to resonate at a second frequency. As such, the resonant frequency of the first and the second piezoelectric element must not be harmonics of each other. In addition, requiring both first and second piezoelectric elements to be stimulated simultaneously in order to deliver the pacing pulses, adds a safety feature to theimplantable pacing electrode18, as the chances of having an external source of mechanical energy capable of resonating both the first and the second piezoelectric elements simultaneously is significantly less than encountering a single external source that would resonate either the first or the second piezoelectric element.

In an alternative embodiment, the first frequency is used to cause the first piezoelectric element to charge the capacitor. The second frequency is then used to control a switch to cause the capacitor to supply a pacing level pulse to the anode and cathode of theimplantable pacing electrode18. One aspect to this use of a second frequency is that the risk of inappropriate release by external ultrasonic sources is reduced since the external source would now need to match two dissimilar frequencies instead of just one. For these concepts, the implanted device would be adapted to produce ultrasonic transmissions at both frequencies.

In a further embodiment, theimplantable pacing electrode18 has two or more piezoelectric elements, where each piezoelectric element has a different resonance frequency. The two piezoelectric elements are coupled to the pacing control circuitry where each of the two or more piezoelectric elements receive mechanical signals from the transmission element, or elements, to charge the capacitor. In one embodiment, the transmission element, or elements, continuously transmit ultrasonic energy that is suitable for resonating each of the piezoelectric elements. As each of the piezoelectric elements are excited they generate electrical energy to charge the capacitor which is coupled within the pacing control circuitry.

In one embodiment, when a pacing pulse is to be delivered to the heart one or more of the transmission elements stop transmitting for a predetermined time interval. In one embodiment, a switch coupled to the piezoelectric elements and the discharge capacitor monitors the continuous flow of energy from the piezoelectric elements. When the flow of one or more of the elements is interrupted for more than the predetermined time interval the switch triggers the capacitor to discharge a pacing level pulse of energy between the anode and cathode of theimplantable pacing electrode18.

Alternatively, the switch is adapted to monitor the ultrasonic transmission for breaks, or interruptions, in the ultrasound transmission. When the switch detects an interruption in the transmission greater than the predetermined time interval the switch controls the capacitor to discharge a pacing level pulse of energy between the anode and cathode of theimplantable pacing electrode18. In one embodiment, the predetermined time interval is a programmable value in the range of ten (10) to fifty (50) milliseconds, with 10 milliseconds being an acceptable value.

In an additional embodiment, the switch controls the capacitor to supply a pacing pulse once the switch detects a sudden increase of ultrasonic intensity in one or more of the multiple frequencies. Alternatively, the switch detects sudden increases in the energy output of one or more of the piezoelectric elements due to a sudden increase of ultrasonic intensity in one or more of the multiple frequencies. Once the switch detects one or more of these sudden increases, it controls the capacitor to supply pacing pulses. Alternatively, the switch could be adapted to detect a combination of breaks and increases at the different frequencies which would signal a pacing pulse is to be delivered. Finally, a transmission at an entirely different frequency which creates a signal from an additional piezoelectric element could be used to trigger the delivery of a pacing pulse.

Referring now to FIG. 8, there is shown an additional embodiment of the present subject matter. As previously discussed, theimplantable pacing electrode18 had been controlled by activating the ultrasound transmission for a short duration (about two milliseconds) to generate and deliver a pacing level pulse and then off for the remainder of the cardiac cycle. In the present embodiment, the ultrasound transmission is continuous so as to provide a continuous source of mechanical energy (or power) to the receiving element, or elements, within theimplantable pacing electrode18.

FIG. 8 shows one embodiment ofpacing control circuitry800, which includes at least onepiezoelectric element802. Thepacing control circuitry800 further includes acapacitor806 and aswitch810. In one embodiment, thecapacitor806 is adapted to store the electrical energy generated as thepiezoelectric element802 receives the continuous ultrasound transmissions. The energy stored in thecapacitor806 is then used to provide pacing pulses across the anode and cathode of theimplantable pacing electrode18. In one embodiment, the energy from thecapacitor806 is used to deliver the pacing level pulses when the continuous ultrasound transmission to thepiezoelectric element802 is interrupted for a predetermined time interval. In one embodiment, theswitch810 monitors the continuous flow of energy from thepiezoelectric element802. When the flow is interrupted for more than the predetermined time interval theswitch810 triggers thecapacitor806 to discharge a pacing level pulse of energy between the anode and cathode of theimplantable pacing electrode18.

Alternatively, theswitch810 is adapted to monitor the ultrasonic transmission for breaks, or interruptions, in the ultrasound transmission. When theswitch810 detects an interruption in the transmission greater than the predetermined time interval theswitch810 controls thecapacitor806 to discharge a pacing level pulse of energy between the anode and cathode of theimplantable pacing electrode18. In one embodiment, the predetermined time interval is as previously described.

In an additional embodiment, it is possible to use two or more frequencies in a multiplexed fashion, where each of the frequencies resonates a separate piezoelectric element contained within two or moreimplantable pacing electrodes18. The ultrasonic transmissions at the different frequencies are interleaved thus sharing the burden of charging the capacitor element in eachimplantable pacing electrode18. The triggering of the pacingelectrode18 to deliver pacing pulses is then accomplished by simultaneously transmitting a combination of frequencies which is specific for signaling an individualimplantable pacing electrode18 to deliver a pacing pulse.

Referring now to FIG. 9, there is shown an embodiment of the present subject matter. FIG. 9 shows a representation of a firstultrasonic transmission900, a secondultrasonic transmission910, and a thirdultrasonic transmission920 being transmitted to a first, second and third implantable pacing elements. At900, the first ultrasonic transmission is shown being pulsed at a first frequency, where the first frequency resonates the first implantable pacing element within each of the transmission elements causing it to generate electrical energy. At910, the second ultrasonic transmission is shown being pulsed at a second frequency, where the second frequency resonates the second implantable pacing element within each of the transmission elements causing it to generate electrical energy. Finally, at920 the third ultrasonic transmission is shown being pulsed at a third frequency, where the third frequency resonates the third implantable pacing element within each of the transmission elements causing it to generate electrical energy. In one embodiment, the first, second and third ultrasonic transmissions are staggered so that at any given time only one transmission is occurring, but the overall effect is to cause a continuous flow of electrical energy to be generated by the implantable pacing element.

Each of the transmissions serve to resonate one of the three piezoelectric elements in each of three implantable pacing elements. This results in the charging of the capacitor in each of the implantable pacing elements. When the implantable pacing elements are to be used to deliver pacing pulses different combinations of two of the frequencies are used to trigger the implantable pacing elements to deliver a pacing pulse. For example, the first implantable pacing element is triggered to deliver a pacing pulse when the firstultrasonic transmission900 and the second ultrasonic transmission occur together910, as shown at940. In the same manner, the second implantable pacing element is triggered to deliver a pacing pulse when the secondultrasonic transmission910 and the thirdultrasonic transmission920 occur together, as shown at950. Finally, the implantable pacing element is triggered to deliver a pacing pulse when the firstultrasonic transmission900 and the thirdultrasonic transmission920 occur together. This embodiment, therefore, allows for pacing to occur at two or more remote sites, where each of the remote pacing sites can be individually controlled by the combination of ultrasonic transmissions.

Alternatively, two or more implantable elements could be implanted in the same general location within the heart. By providing each of the two or more implantable elements with three or more piezoelectric elements that have individual resonance frequencies, ultrasonic transmissions can be delivered to continuously charge the capacitors. Additionally, each element can also be individually controlled to provide a pacing pulse. This allows for a first element to be discharged while the second element continues to charge. The first element then “skips” the next required pacing pulse as the second element is triggered to deliver the pulse. This allow for a longer time (e.g., a two cardiac cycle charging time) for each of the elements to prepare for delivering a pacing pulse. When three elements are used in a particular location, the present embodiment would allow for a three cardiac cycle charging time.

The energy that is accumulated and then triggered for release as a pacing stimulus does not necessarily need to come from the ultrasonic source in the implanted device. Rather it could be locally at the remote pacing element. For example, the mechanical action of the contracting heart could be utilized to produce electrical energy by compressing or deflecting a piezoelectric element that would serve to produce the charge for storage in a capacitor. It is also possible that high-frequency (10 to 50 kHz) low-voltage AC electrical signals could be passed over the heart by the implanted device. Because of the high-frequency, and low voltages, these signals would not excite the myocardial tissue. However, the remote pacing site could rectify the signals locally and use it as an energy source for charging a capacitor. In this arrangement, it makes sense for the two (or more) electrodes at the remote pacing site to be further apart so as to capture as much of the high-frequency AC field as possible. This could be accomplished by having the electrodes in the forms of short flexible wires.

Claims (17)

What is claimed is:

1. A system comprising:

a first piezoelectric element which converts mechanical energy into electrical energy, the mechanical energy which originates from a source external to an implantable electrode;

a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode; and

an implantable housing which includes a peripheral surface, where the first piezoelectric element is integrated with the housing, and the anode and the cathode are positioned at opposite sides on the peripheral surface of the housing.

2. The system ofclaim 1, further comprising pacing control circuitry coupled to the first piezoelectric element, the anode and the cathode such that the pacing control circuitry receives electrical energy generated by the first piezoelectric element and delivers pacing pulses between the anode and the cathode.

3. The system ofclaim 1, wherein the implantable housing includes an active fixation element.

4. A system comprising:

a first piezoelectric element which converts mechanical energy into electrical energy, the mechanical energy which originates from a source external to an implantable electrode;

a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode;

pacing control circuitry coupled to the first piezoelectric element, the anode and the cathode, where the pacing control circuitry receives electrical energy generated by the first piezoelectric element and delivers the pacing level energy pulse between the anode and the cathode;

where the pacing control circuitry includes:

a switch, where the switch is operated by the electrical energy generated by the first piezoelectric element; and

a potential energy source, where the potential energy source is coupled to the switch and supplies electrical energy to be delivered between the anode and the cathode once the first piezoelectric element provides electrical energy to activate the switch.

5. The system ofclaim 4, wherein the potential energy source is an electrochemical battery.

6. The system ofclaim 4, wherein the switch is a metal oxide field effect transistor.

7. A system comprising:

a first piezoelectric element which converts mechanical energy into electrical energy, the mechanical energy which originates from a source external to an implantable electrode;

a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode;

pacing control circuitry coupled to the first piezoelectric element, the anode and the cathode, where the pacing control circuitry receives electrical energy generated by the first piezoelectric element and delivers the pacing level energy pulse between the anode and the cathode; and

an implantable housing having a peripheral surface, where the pacing control circuitry is mounted within the housing, the first piezoelectric element is integrated with the housing, and the anode and the cathode are positioned at opposite sides on the peripheral surface of the housing.

8. The system ofclaim 7, wherein the implantable housing includes a second piezoelectric element which converts mechanical energy into electrical energy.

9. The system ofclaim 8, wherein the second piezoelectric element has a different resonance frequency than the first piezoelectric element.

10. A system comprising:

a first piezoelectric element which converts mechanical energy into electrical energy, the mechanical energy which originates from a source external to an implantable electrode;

a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode;

a second piezoelectric element which converts mechanical energy into electrical energy, where the first piezoelectric element resonates at a first frequency range and the second piezoelectric element resonates at a second frequency range; and

a switch and a capacitor, where the switch is coupled to the first piezoelectric element, the second piezoelectric element, the anode and the cathode, and the capacitor is coupled to the switch, where electrical energy is generated by the first piezoelectric element when a first transmission at the first frequency range resonates the first piezoelectric element and electrical energy is generated by the second piezoelectric element when a second transmission at the second frequency range resonates the second piezoelectric element, where the electrical energy is stored in the capacitor and the switch causes the pacing level energy pulse to be delivered between the anode and the cathode when a predetermined pulse signal is detected.

11. The system ofclaim 10, where the predetermined pulse signal is a predetermined frequency change in the first frequency range.

12. The system ofclaim 10, where the predetermined pulse signal is a predetermined frequency change in the first and second frequency ranges.

13. A system comprising:

a first piezoelectric element which converts mechanical energy into electrical energy, the mechanical energy which originates from a source external to an implantable electrode;

a cathode and an anode, where electrical energy generated by the first piezoelectric element causes a pacing level energy pulse to be delivered between the anode and the cathode; and

where the source includes a catheter having a transmission element adapted to transmit the mechanical signals to the first piezoelectric element, and a pulse generator, where the pulse generator includes a transmission circuit and where the transmission element is coupled to the transmission circuit to generate and transmit the mechanical energy to the first piezoelectric element.

14. The system ofclaim 13, where the transmission element transmits energy in a low frequency range of approximately one to five megahertz.

15. A method, comprising:

transmitting mechanical energy from a source external an implantable electrode;

receiving the mechanical energy within the implantable electrode;

generating electrical energy within the implantable electrode from the mechanical energy;

delivering pacing level energy pulse across an anode and a cathode positioned on the implantable electrode when the electrical energy is generated; and

where causing the pacing level energy pulse includes:

generating a switching signal from the electrical energy;

transmitting the switching signal to a switch coupled to a potential energy source; and

receiving the switching signal to activate the switch.

16. The method ofclaim 15, wherein delivering pacing level energy pulses across the anode and the cathode includes causing energy stored in a capacitor to be delivered to the anode and the cathode once the switch has been activated.

17. The method ofclaim 15, wherein delivering pacing level energy pulses across the anode and the cathode includes using energy created by the half-cell potential difference between metal of the anode and metal of the cathode.

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